Recently, owing to remarkable progress of ink jet printers and plotters, minute images of full color can be easily obtained.
Ink jet recording systems perform recording of images or letters by ejecting ink droplets according to various operational principles and depositing them on recording materials such as paper. The ink jet printers or plotters recently rapidly spread in various uses as apparatuses for making hard copies of image information such as letters and various figures produced by computers. Particularly, color images obtained by multicolor ink jetting systems are not inferior in quality to the recorded images obtained by the multicolor printing according to plate making systems or the color photographic processes. Moreover, when a small number of prints are to be produced, they can produce the prints more cheaply than the printing process or photographic process. Thus, ink jet recording systems are being widely applied to the field of multicolor image recording.
Moreover, with diversification of uses, use of them for preparation of large-sized posters and POP arts and for drafting has increased. In these uses, satisfactory images can be obtained due to utilization of high sharpness and excellent color attainable by ink jet recording, resulting in a high propaganda effect. Application to these uses increases because images excellent in image reproducibility or color reproducibility such as sharpness and colorfulness can be easily obtained on personal computer level, and this is a reason for making much use of ink jet recording materials.
Owing to enhancement of performance and diversification of these ink jet recording apparatuses, needs for ink jet recording increase and, as a result, characteristics and demands required for recording apparatuses and ink jet recording materials are also considerably enhanced. For example, in the case of the uses for large-sized posters or POP arts and the uses for outputting photographic images, these uses are indoor or outdoor displays or personal recording and storage, and, hence, weathering resistance and storage stability of images higher than those of conventional technologies are demanded. For these demands, improvement in inks and ink jet recording materials has been advanced and considerably higher storage stability has been attained. However, light resistance has not yet reached the level of silver salt photography and thus the demands have not yet been satisfied.
In order to satisfy these demands, recently, inks of pigment type are used. It is known that since the pigment inks are less in deterioration by light and do not redissolve in water, weathering resistance and storage stability of the resulting images are higher than those of the images obtained with inks of dye type. However, since the colorant pigment in the inks is insoluble in solvents, being different from dyes, the colorant pigment in the inks must be stably dispersed and the proportion of the colorant pigment in the ink cannot be easily increased. Furthermore, the pigment inks are not so high in coloring efficiency as the dye inks and can hardly give clear colors.
Therefore, naturally the demand for ink jet recording materials also increases. As a method for improving absorbability for pigment ink, it is considered to increase thickness of the ink-receiving layer coated on a support. According to this method, the ink absorbability can be improved, but color developability deteriorates because the ink deeply penetrates in the direction of base paper. As mentioned above, the pigment ink cannot develop clear color as compared with dye ink, and hence in the case of the pigment ink, the color developability is considerably deteriorated when the ink deeply penetrates. Furthermore, the deterioration is further conspicuous in the case of ink jet recording materials having no ink-receiving layer.
For obtaining satisfactory ink jet recording performance, there is proposed an ink jet recording material which contains inorganic ultrafine particles, and there is disclosed an ink jet recording material which uses synthetic silica having a primary particle diameter of 3-30 nm and prepared mainly by a gas phase method (see, for example, Patent Documents 1 and 2). Furthermore, there is disclosed a method of providing a coat containing inorganic ultrafine particles, polyvinyl alcohol and boric acid or a salt thereof on an ink solvent non-absorbent support (see, for example, Patent Documents 3-5). According to this method, the coat can be obtained without causing occurrence of cracking if the dry coating amount of the coat is small, but the coat is low in ink absorbability, and in order to provide a thick coat to improve the ink absorbability, it is necessary that a coating solution is coated after heating the solution to higher than room temperature or the coat is cooled after coating, thereby to set the coating solution on the support to form a firm bond between a viscosity increasing agent and inorganic ultrafine particles or a binder, followed by carrying out drying. Therefore, the production efficiency lowers and besides even if the coat is made thicker, the ink absorbability is sometimes unsatisfactory.
For obtaining an ink jet recording material which aims at attaining both the color developability of pigment ink and the ink absorbability, it is proposed to coat, on an ink solvent non-absorbent support, a first ink-receiving layer containing a gas phase process silica, boric acid or a borate and polyvinyl alcohol and a second ink-receiving layer containing alumina or an alumina hydrate, boric acid or a borate and polyvinyl alcohol in succession (see, for example, Patent Document 6). According to this method, an improvement of ink absorbability can be attained, but it is still insufficient.
For improving the ink absorbability, it may be considered to provide an ink-receiving layer having the above construction on a support having gas permeability and ink solvent absorbability such as a paper support. However, in the case of using an ink solvent non-absorbent support, a binder component or the like in the coat does not fall into the support and, hence, cracking of the coat does not occur while in the case of using a support having ink solvent absorbability such as a paper support, the binder component or the like in the ink-receiving layer falls into the paper support and cracking of the surface of the ink-receiving layer is apt to occur. The cracking of the coating layer becomes conspicuous when an ink-receiving layer comprising a fine particle pigment of several ten nm to several hundred nm in particle diameter is used for the purpose of imparting gloss. There is the problem that when the pigment ink falls into the cracks, color developability lowers to deteriorate the pigment ink characteristics.
In order to enhance color developability and fixability of pigment ink, it is proposed to use an alumina hydrate as a pigment used in the ink-receiving layer (see, for example, Patent Document 7). The color developability and fixability of pigment ink are improved according to this method, but there is a problem that even if a paper support of high absorbability is used, the ink absorbability is insufficient.
On the other hand, there is proposed an ink jet recording material in which a silica porous layer is provided as a lower layer and a layer containing alumina or alumina hydrate is provided as an upper layer or a recording material in which an absorbent layer containing a pigment is provided as a lower layer and a layer containing pseudoboehmite is provided as an upper layer (see, for example, Patent Documents 8 and 9).
When the upper layer containing inorganic ultrafine particles is formed by coating a coating solution of the upper layer on a lower layer comprising porous silica and drying the coat, the inorganic ultrafine particle component or the like in the upper layer falls into the lower layer. As a result, cracking of the surface of the upper layer is apt to occur to cause reduction of surface gloss, and, furthermore, when a dye ink is used in ink jet recording, ink absorbability is improved due to many cracks, but in the case of using a pigment ink lower in color developability than the dye ink, the pigment ink falls into the cracks, which may cause deterioration of pigment ink characteristics.
Furthermore, an ink jet recording material is proposed which comprises an undercoat layer containing a basic material provided for improving color developability of ink and a porous image receiving layer comprising fumed alumina provided on the undercoat layer (see, for example, Patent Document 10).
However, since the undercoat layer containing a basic material comprises only a polymer component such as gelatin, the polymer component is swollen with water contained in the porous image receiving layer during coating of the porous image receiving layer, and strain occurs during drying of the porous image receiving layer, which may cause cracking of the porous image receiving layer and reduction of gloss and deterioration of the pigment ink characteristics.
[Patent Document 1] JP-A-10-203006 (pages 3-9)
[Patent Document 2] JP-A-8-174992 (pages 3-6)
[Patent Document 3] JP-A-7-76161 (pages 2-3)
[Patent Document 4] JP-A-10-193777 (pages 2-10)
[Patent Document 5] JP-A-2002-2094 (pages 2-10)
[Patent Document 6] JP-A-2002-225423 (pages 2-7)
[Patent Document 7] JP-A-2002-79748 (pages 2-4)
[Patent Document 8] JP-A-6-55829 (pages 2-3)
[Patent Document 9] JP-A-7-89216 (pages 2-6)
[Patent Document 10] JP-A-2002-331746 (pages 3-5)